A method and an apparatus according to the state of the art are now explained by reference to FIG. 1. The method is carried out on an engine 10 which has an injection arrangement 11 in its suction channel and a lambda probe 12 in its exhaust-gas channel. A signal TI, which is a measure of the injection time, is fed to the injection arrangement 11. This signal TI is formed from a provisional injection-time signal TIV (n, L) by logical combination with various correcting variables. As a rule, the provisional value for the injection time is read out from a characteristic field in which such values are stored as a function of values of the engine speed n and a load-dependent variable L. The logical combination takes place in a logic routine 13, in which the various correcting variables act on the particular values present by multiplication, addition or subtraction, depending on the type of variable.
The signal from the lambda probe 12 is fed as a lambda actual value to a subtraction step 14 and there it is subtracted from a lambda desired value. The control deviation thus formed is processed in a control unit 15, thereby producing as a regulating value a control factor FR. This control factor FR, on the one hand, is fed directly to the logic routine 13 and, on the other hand, serves for adaptation purposes. Via a change-over switch 16 which is shown as hardware in FIG. 1, but in practice is realized in software form, the control factor FR is alternately fed first to a mixture adaptation routine 17 for a period of time of, for example, 60 seconds and then to a charge-factor adaptation routine 18 for 90 seconds. The mixture adaptation routine 17 forms various correction values, for example those for compensating for injection-time errors caused by leakage air, by changes of air pressure or by changes in the performance of the injection arrangement 11.
The charge factor FTEAD adapted in the charge-factor adaptation routine 17 does not directly form a value usable in the logic routine 13, but is multiplied by a gas-volume value GV in a multiplication step 19. The multiplication value FTEA serves in the logic routine 13 as a value to be subtracted. The gas-volume value GV is read out from a characteristic field 20 as a function of values of the engine speed n and of the throttle flap angle DK.
Adaptation methods in lambda-control systems take place relatively slowly. Attempts are therefore made to store adapted values when the controlled internal combustion engine stops, so that they are available immediately at the next restart and the lengthy adaptation process does not have to be executed from the outset again. In this connection, when the internal combustion engine is switched off, the last value of the charge factor FTEAD is stored in a non-volatile memory (NV-RAM) 21. The stored value FTEADS is read out at the restart of the engine and is fed to the charge-factor adaptation routine 17 as an initial value for adaptation.
In practice, it repeatedly happens that a vehicle engine is switched off in the hot state in warm weather and a restart is effected again only with the engine cold and sometimes in considerably colder weather than before. When the engine is hot in warm weather, the charge factor FTEAD is approximately at the value 1, that is almost the entire tank-venting gas is fuel gas. In contrast, when the engine is cold in cold weather, the charge factor FTEAD corresponds essentially to the value 0, that is the tank-venting gas is almost exclusively zero, that is it contains scarcely any fuel gas. If the charge factor has first been adapted to the value 1 and, when the engine is restarted, this value is then used as a new initial value for the adaptation, even though the value 0 would actually be appropriate, the internal combustion engine initially receives far too little fuel before the control 15 provides sufficient compensation. Because of this, there is the possibility that, at the first transition to tank-ventilation adaptation, the engine will die or then run very roughly.